The present invention relates to semiconductor lasers. In particular, the present invention relates to master oscillator grating coupled power amplifiers (MOGCPAs).
Master oscillator power amplifiers (MOPAs), as shown in FIG. 1, typically include a semiconductor Distributed Feedback (DFB) laser diode 101 acting as a master oscillator optically coupled to a tapered optical power amplifier 102. The diode laser and amplifier are essentially a single unit with an integrated optical alignment.
MOPAs are known to have potential to provide both high power and a diffraction-limited single-mode output. MOPA designs that produce a high-power single-mode output, however, have a variety of weaknesses. For example, to achieve a single-mode output, the master-oscillator section of the device is very narrow. This often results in the device exhibiting a large lateral beam divergence, thereby requiring an astigmatic lens for practical use. For example, known MOPA devices can exhibit as much as 15 to 20 degrees beam divergence in the lateral direction, creating at least two problems. First, the divergent beam with a wide output aperture requires complicated focusing optics. Second, the divergent beam propagating in the amplifier section requires an amplifier section with a wide aperture. Since the length of the tapered section must not be shorter than 1 mm to provide the amplification, the output aperture can not be narrower than 50-350 xcexcm. Additionally, known designs also tend to exhibit self-focusing and filamentation problems that limit the level of diffraction-limited power and degrade device stability.
Variations of MOPAs have been conceived, but all contain unacceptable shortcomings.
For example, FIG. 2 is a schematic diagram detailing a Master-Oscillator Deflector-Amplifier Grating for Surface Emission (GSE). In this figure, a laser beam generated in master-oscillator section 201 couples directly into deflector-amplifier section 202, which lies along the same axis as master-oscillator section 201. Deflector-amplifier section 202 contains tilted Bragg grating deflector 204. Deflector-amplifier section 202 is optically coupled to GSE section 203 through tilted grating 204, which scatters the laser beam into GSE section 203. GSE section 203 has a grating that scatters the generated laser beam in the direction perpendicular to the structure plane. Thus, this configuration utilizes three regions, with a coupling grating found inside deflector-amplifier section 202, and light is emitted perpendicular to the direction of propagation through the amplifier section. This apparatus, however, has the drawback that, to maintain single-mode operation, deflector-amplifier amplifier section 202 must be the same width as master-oscillator section 201, thereby limiting output.
FIGS. 3A and 3B is a configuration of the previously-discussed apparatus in which power is amplified by the addition of post amplifier 302. This configuration has the drawback that, because of the refractive index step at the interface between post amplifier 302 and GSE 303, multimode lasing in the direction perpendicular to the axes of the deflector-amplifier section occurs.
FIG. 4 is an apparatus that employs the basic design shown in FIG. 2, but includes beam splitters between master-oscillator section 401 and deflector-amplifier sections 402a-402d. The splitters allow for additional GSE sections 403a-403d. Power output is not improved, however, because beam splitters 401a divide the available energy and introduce additional losses.
FIG. 5 is the same as the apparatus discussed in FIG. 2, except that GSE 503 is rotated at an angle xcexa9 relative to deflector-amplifier section 502. This configuration has drawbacks similar to the configuration displayed in FIG. 2.
FIG. 6 displays a variety of embodiments that include laser or lasers 601 and GSE 602. These configurations do not include a broad-contact xe2x80x9cpower supplyingxe2x80x9d section, and are not limited to a single-mode output.
Thus, a need exists for a type of MOPA with low lateral beam divergence, and which is stable at high power output with a narrow output aperture.
To alleviate the problems inherent in known MOPAs, the present invention introduces a master oscillator grating coupled power oscillator (MOGCPA) with a power-oscillator section at an angle to the optical cavity in the master-oscillator section.
In one embodiment of the present invention, the MOGCPA contains a single-mode-master-oscillator section with a waveguide defined by a first end and a second end, the first end including a first distributed Bragg reflector mirror, and the second end including a second distributed Bragg reflector mirror, the single-mode-master-oscillator section having a first longitudinal axis. The MOGCPA additionally contains a broad-contact-amplifier section coupled to said single-mode-master-oscillator section by a coupling grating, said broad contact amplifier section including a reflection side, an output side and a second longitudinal axis, the second longitudinal axis being at an angle approximately (90xc2x0xe2x88x92xcex2) to said first longitudinal axis, xcex2 being in a range between 0xc2x0 and approximately 20xc2x0.